Master Yi is often builded as squichy dps with some life steal to not die in a second. However, he is dead when stunned, because he cannot return his life then. He is also focused at first, so he will not do any damage.
How about Yi with 4k health, 200 armor and 150 magic resist and resurrection? Squishy? I don't think so. He also deals massive damage with 350 ad, trinity force, infinity edge and 60% critical chance. It does about 1.3k damage per hit.
Pretty amazing, huh?

Marks and Quintessences are flat armor penetration for more damage. Seals and Glyphs are health and magic resist per level for better survival.
I use standard 21/0/9 mastery tree for ad carry.
I think it's easy to understand.

Exhaust - Great spell for chasing and reducing enemy's damage.


Ghost - Also good for chasing and escaping.

I always start with Doran's Shield, which provides health, armor and health regeneration. Good for early game.


Then I buy Mercury's Treads for some magic resist, tenacity and movement speed.


Sheen is very important for this build. 100% more damage for auto-attack, when any ability was used. Now you can attack with this sequence: Alpha Strike => Auto-attack => Wuju Style => Auto-attack => Highlander => Auto-attack...'


Zeal gives more movement speed and easier farming. It doesn't need to explain.


Trinity Force is awesome. 150% damage instead of 100% additional damage after using any ability, more movement speed, attack speed, critical chance and chance for slow enemy.


Infinity Edge just provides a lot of damage. It's self-explanatory.


Warmog's Armor isn't often bought for Master Yi, but it's very good item for him, because of easy farm. This is instead of life steal, which is useless, when u can't do damage (stun or something). Huge survival.


Atma's Impaler makes Warmog's Armor even better choise. Think about additional 80 damage, more critical damage and armor.


I usually buy Guardian Angel, which gives even more survival and resurrection (WuJu become Kamikadze? ^^). However, this is situational item.

Guardian Angel is great, when enemy team is balanced. However, if you smash them to the ground, you don't need it.


Phantom Dancer gives you even more dps and movement speed. Good item for map control and chasing.


Youmuu's Ghostblade has similar usage as Phantom Dancer.


If you want more health, buy Frozen Mallet, which also gives you 35 attack damage (with Atma's Impalier) and slows enemys.


When you have problems with enemy's attack damage, buy Randuin's Omen. More armor, health regeneration, chance to reduce enemy's attack speed, when they hit you and when you activate it, it slows nearby enemy champions for about 2.5 sec and also reduce their attack speed for this duration.


If you have other ad carrys in your team and noone has Stark's Fervor then get it. It buffs nearby alies by life steal, health regeneration and attack speed. Also it reduce enemy's armor.


Problem with nukers? Buy Force of Nature, which gives you much magic resistance, massive health regeneration and more movement speed.


If you are afraid of crowd control, take Banshee's Veil. It blocks one negative spell and provides some magic resistance.


When enemy champions like stick together tough, Tiamat would do massive damage with additional 50 damage, because 50% goes to nearby champions. Also gives some health regeneration.